Using transmission electron microscopy a study was made of this material, which exhibited a huge dielectric response, at up to kHz frequencies, over a wide range of temperatures. In both single crystals and in polycrystalline samples, including sintered bulk and thin films, there was no sign of the twin domains that had been suggested. However, in single crystals, there was a very high density of dislocations with a Burgers vector of [110]; as well as regions with cation disorder and planar defects with a displacement vector of ¼[110]. In polycrystalline samples, many grain boundaries with an O deficiency, in comparison with the grain interior, were observed. The defect-related structural disorder and inhomogeneity, which served as an internal barrier layer capacitance in a semiconducting matrix, was suggested to explain the very large dielectric response of the material. A transmission electron microscopic study of the structural defects supported a proposed morphological model which involved percolating conducting regions and blocking regions.

Defect Structure of the High Dielectric Constant Perovskite, CaCu3Ti4O12. L.Wu, Y.Zhu, S.Park, S.Shapiro, G.Shirane, J.Tafto: Physical Review B, 2005, 71[1], 014118 (7pp)